I had to euthanize my very first fish today... and it was just a feeder comet! for some reason my shark befriended it, and never ate it! it lived for close to a month, and today i found it stuck to the filter, and the filter had actually pulled one of it's eyes off.
i knocked it off the filter, and it kind of started to swim, but not really. i netted it out, put it in a brown plastic bag, and **** it with one of my college text books (Cisco CCNA 3 & 4... a huge book).
it was hard even though it wasn't what i consider to be one of "my fish," and was purchased to die anyways. but still a tough thing to do!